Our long-term objective is to locate the brain stem neurons which generate the respiratory pattern in the cat. We have applied power spectral analysis to respiratory motor nerves and brain stem neurons. We have identified a 90Hz spectral peak in the electrical activity of the phrenic nerve and of the recurrent laryngeal nerve during inspiration. The phrenic nerve has a second spectral peak at 55Hz. We suspect that the 90Hz peak is associated with the dorsal respiratory group of the ventrolateral nucleus of the tractus solitarius. From whole body coooling experiments, we have found that the 90Hz peak is quite temperature sensitive; in six cats, the temperature sensitivity was 5.00 plus or minus 1.08 Hz/degC. Using focal cooling in the brain stem, we will determine whether the high frequency synchrony of the inspiratory activity is a local or global property of the respiratory neuronal network. With these studies we hope to locate areas in the medulla and pons to explore with microelectrodes for neurons of the central respiratory pattern generator.